1. Field of the Invention
The present invention relates to an image communication apparatus, a method of controlling the same, and a storage medium, and more particularly to a control technique for use in transmitting image data to a transmission destination by facsimile transmission according to SIP (session initiation protocol).
2. Description of the Related Art
Besides a conventional facsimile transmission technique using a public switched telephone network (PSTN), there have been proposed a facsimile transmission technique using a LAN (local area network), which enables high-speed transmission and is configured to be compatible with the facsimile transmission technique using the public switched telephone network. For example, according to ITU-T Recommendation T.38, point-to-point transmission is achieved on a LAN and hence a LAN is used as a transmission path and SIP (session initiation protocol) is used as a call control unit. For example, there has been proposed a network called the NGN (next generation network), for achieving telephone service, video communication service, and the like, using SIP. On the NGN, it is possible to provide band guarantee, phone number authentication, and so forth, to thereby perform high-speed and secure image transmission.
PSTN transmission speed is 33.6 kbps maximum, whereas the NGN guarantees a transmission speed of 1 Mbps maximum. Therefore, the NGN can realize approximately 30 times faster transmission speed. For example, the use of the NGN enables transmission of a high-definition and high-resolution image or color image, which has not been welcomed because of a long transmission time and a high communication charge, to be performed in a short time and for a small communication charge.
Further, ITU-T Recommendation T.38 is compatible with ITU-T Recommendation T.30 used on the PSTN. For this reason, transmission is possible between an image communication apparatus to which is applied ITU-T Recommendation T.38 (hereinafter referred to as “the T.38-based apparatus”) and an image communication apparatus to which is applied ITU-T Recommendation T.30 (hereinafter referred to as “the T.30-based apparatus”). This transmission can be achieved by providing a T.38 gateway (GW) for interconversion between T.38 and T.30, between a LAN line, such as the NGN and the conventional PSTN.
However, the capabilities of the T.30-based apparatus are reflected on the transmission speed and hence the transmission speed cannot exceed 33.6 kbps. Transmission on a LAN between T.38-based apparatuses can be performed at a high speed for a small charge, but transmission from the T.38-based apparatus to the T.30-based apparatus cannot be performed at a transmission speed higher than 33.6 kbps, so that transmission has to be performed at a low speed for a high charge as in the prior art. Further, due to transmission performed at a low speed, the communication line is occupied, which makes it impossible to perform other transmission until the occupied state of the communication line is over.
To solve this problem, there has been proposed e.g. a technique of changing control based on whether or not transmission is to be performed between T.38-based apparatuses (see e.g. Japanese Patent Laid-Open Publication No. 2002-111952). According to this publication, in a case where facsimile transmission is performed from a T.38-based apparatus, the T.38-based apparatus detects whether a transmission destination apparatus is a T.38-based apparatus directly connected to a LAN or a T.30-based apparatus connected to the LAN via a gateway. Then, according to a result of the detection, a signal wait time period specified in T.30 or T.38 associated with a detected type of the transmission destination apparatus is selected (when the transmission destination apparatus is a gateway connected type, a longer wait time period is selected so as to compensate for a time lag that occurs when the transmission is performed via the gateway). Note that Japanese Patent Laid-Open Publication No. 2002-111952 relates only to the technique of compensating for a lag time that occurs when a gateway is interposed, to thereby stabilize communication, but it makes no mention of image control (i.e. control of image quality and a color image) to which the present invention is directed.
In a case where a high-resolution image or a color image is transmitted from the T.38-based apparatus, when a transmission destination apparatus is directly connected to a high-speed communication line (LAN or NGN), it is possible to achieve high-speed transmission for a small charge. However, when a transmission destination apparatus is a T.30-based apparatus that is not directly connected to a LAN (NGN), transmission is performed at the same transmission speed as the conventional PSTN transmission speed, i.e. at a low speed. As a consequence, the communication line is occupied for a long time period and a high communication charge has to be paid.